1. Field of the Invention
The present invention generally relates to a multi-processor system having a plurality of processors connected to duplicated ring-type communications buses, and more particularly to a fault control system for such communications buses.
2. Description of the Related Art
A multi-processor system is known in which a plurality of processors are coupled to duplicated ring-type or bus-type communications buses via adapters (hereinafter referred to as stations). Generally, a single supervisory station having a supervisory function, and a plurality of supervised stations are provided in each of the ring-type communication buses. If a fault has occurred in one of the supervised stations, the station in which the above fault has occurred must be disconnected from the communications buses. If a fault has occurred in the supervisory station, the supervisory function is lost.
FIG. 1A is a block diagram of a conventional multi-processor system, which comprises two ring-type communication buses #0 and #1, and processors A, B, C and D. Bus adapters (hereinafter referred to as stations) 70a, 71a, 72a and 73a are provided in the ring bus #0, and bus adapters (stations) 70b, 71b, 72b and 73b are provided in the ring bus #1. When there is no fault, the processors A-D respectively execute load-decentralized processes, such as control of an exchange. Data, status information and instructions are transferred between the processors A-D via the stations and the ring buses #0 and #1. During this operation, the processors A-D respectively use both the ring buses #0 and #1 so that transfer of information is decentralized. In this case, the ring buses #0 and #1 are selectively used on the basis of the types of pieces of information.
The bus ring #0 has a single supervisory station, and a plurality of supervised stations. In FIG. 1A, the station 72a functions as a supervisory station. Similarly, the ring bus #1 has a single supervisory station, and a plurality of supervised stations. In FIG. 1A, the station 71b functions as a supervisory station.
The supervisory stations respectively provided in the ring buses #0 and #1 have the following three functions. The first supervisory function supervises the configurations of the ring buses #0 and #1. More particularly, topology information, address information, and control parameters regarding the ring buses #0 and #1 are supervised. The second supervisory function periodically gathers pieces of statistical information and traffic information concerning the ring buses #0 and #1. The third supervisory function executes a manual reconfiguration process and a remote test process. More particularly, arbitrary stations are instructed to operate a predetermined process, and a predetermined remote test is carried out for arbitrary stations.
If one of the supervisory stations does not execute the above supervisory functions because of a fault which has occurred therein, the supervisory functions are lost.
FIG. 1B shows a state of the multi-processor system in which a fault has occurred in the supervisory station 71b connected to the ring bus #1 and the processor B. The supervised stations 70b and 72b adjacent to the supervisory station 71b respectively execute a loop-back operation, in which the supervisory station 71b is disconnected from the ring bus #1 and a bus loop including the stations 70b, 72b and 73b is formed. It will be noted that the solid lines indicating the ring buses #0 and #1 respectively include up and down bus lines in practice.
Since the supervisory station 71b is disconnected from the ring bus #1, the above-mentioned first through third supervisory functions for the ring bus #1 cannot be performed, and the ring bus #1 cannot continue to operate normally. It will be noted that the first through third supervisory functions for the ring bus #0 continue to operate irrespective of the occurrence of a fault in the supervisory station 71b because the supervisory station 72a continues to operate normally.